So a new limited time dragon has been added to DragonVale, namely the Butterfly dragon. I see this is a tri-combination dragon using Air, Lightning and Fire. With the last few dragons however simply matching these elements has proven to not be effective. What is a good combination of dragons to produce this type of dragon?

It has been confirmed multiple places that one Firefly dragon is a requirement to breed this dragon. So your options are Firefly + Air or Firefly + Air Hybrid. For Air Hybrids, Sonic and Blazing have both been reported to work. They are probably best, since they do not introduce any new elements.

The answers from @Arremer and @EBongo below contain vital information so I can not accept one over the other, to that end here is that information combined:

Overview information from @Arremer

Popular combinations:

Firefly Dragon + Air dragon

Sonic dragon + Firefly Dragon

You need to be level 14.

Breeding butterfly dragon takes place in a normal breeding cave or on the breeding island.

Breeding time: 12 hours

A specific addition from @EBongo

Firefly is a requirement

It has been confirmed multiple places that one Firefly dragon is a requirement to breed this dragon. So your options are Firefly + Air or Firefly + Air Hybrid. For Air Hybrids, Sonic and Blazing have both been reported to work. They are probably best, since they do not introduce any new elements.